SAN FRANCISCO, June 4 (Reuters) - The state of Washington said on Monday it had sued Facebook Inc and Alphabet Inc's Google for allegedly violating state campaign finance law by failing to maintain information about who buys election ads.

The state's attorney general, Bob Ferguson, who posted copies of the lawsuits here://agportal-s3bucket.s3.amazonaws.com/uploadedfiles/Another/News/Press_Releases/Complaint-20180604-Google.pdf on his website, said he was seeking penalties against the companies and an injunction for failing to disclose ad spending in state elections since 2013.

Facebook said it looked forward to resolving the lawsuit quickly after it recently introduced tools for people to see who is buying political ads on its social network.

A representative for Google could not immediately be reached for comment. Like Facebook, Google has pledged to create an online archive of ads that run on its service.

Facebook and Google have faced criticism from lawmakers, users and advocates for campaign finance regulation for their role in selling political ads after Russians allegedly used fake names to buy ads to sway American voters around the 2016 U.S. presidential election.

Unlike most U.S. jurisdictions, both Washington state and the city of Seattle have laws dating to the 1970s that require companies that sell advertising, such as radio stations, to disclose who buys political ads. Other states put the burden of disclosure on the buyers themselves.

A Seattle official said in February that he thought Facebook was in violation of the city's law, though Seattle has not sued the company.

Ferguson said his office received a citizen complaint in April alleging that Facebook and Google had not provided legally required information on political ads.

Reporting by David Ingram;
Additional reporting by Nate Raymond
Editing by David Gregorio and Leslie Adler